Regional curare for the reduction of the safety factor in human motor end-plates studied with single fibre electromyography.

A method employing six minutes of regional curarization with 0.5 mg D-tubocurarine and single fibre electromyographic measurements (SFEMG) was used in order to study the effect of an additional small dose of D-tubocurarine. The effect of the additional dose was most pronounced in terms of increased jitter, on motor end-plates with the initially highest jitter. The combination of regional curarization and SFEMG jitter recordings offers a sensitive technique for detecting mild effects of various drugs on neuromuscular transmission not detectable with decrement investigations.     

Neuromuscular transmission in myasthenia gravis studied with single fibre electromyography

Patients with myasthenia gravis have been investigated with single fibre electromyography. In all myasthenic muscles recordings were obtained where there was an increase of the jitter and occasional blocking of different degree of single fibre action potentials. The jitter is the variability at consecutive discharges in the time interval between action potentials from two muscle fibres from the same motor unit. During prolonged activity the jitter increased and blockings occurred more and more frequently. The size of the jitter and the degree of blocking also depended on the discharge rate. At a low rate the jitter was lower and the degree of blocking less than at the high rate. Injection of edrophonium could decrease or increase the jitter or leave it unaffected. Single fibre electromyography is a sensitive way of studying the transmission in individual motor end-plates in myasthenia gravis and is also a valuable diagnostic aid.     

Myasthenic syndrome studied with single fiber electromyography.

A patient with the myasthenic syndrome was investigated with single fiber electromyography (SFEMG). It was found that 35 of 36 potential pairs had increased "jitter" and that 29 of these demonstrated impulse blockings. There was improvement in neuromuscular transmission with higher rates of innervation. Transmission worsened following rest. The SFEMG findings at the motor end-plate level correlate well with the results of repetitive stimulation and in vitro studies.     

Cephalic tetanus studied with single fibre EMG.

In a case of cephalic tetanus with left facial spasms and trismus, the repetitive stimulation of the left facial nerve at 3, 10 and 20 Hz showed no facilitation or decrement. The amplitudes of the blink reflex were 50% lower on the affected side. The silent period of the masseter muscles was shortened. Concentric needle examination of the masseters and left facial EMG of the left frontalis muscle showed increased jitter and blocking in a significant proportion of the recorded potentials. Both jitter and blocking improved on higher innervation rates. All electrophysiological findings were normal on the second examination when the patient was asymptomatic. The single fibre EMG findings point to a presynaptic defect in the neuromuscular transmission in human tetanus.     

Pathophysiology of fasciculations in ALS as studied by electromyography of single motor units

Electromyographic potentials of fasciculations were studied in ten patients with amyotrophic lateral sclerosis (ALS). The EMG recordings were made from the extensor digitorum brevis muscle. The EMG recording was so selective that only one motor unit potential appeared on maximal voluntary effort and on supramaximal electrical stimulation of the peroneal nerve. In a series of fasciculations, the shapes of the EMG potentials varied, while in a series of voluntary twitch activations of electrical nerve stimulations the EMG potentials were mainly constant. Fasciculations were followed by antidromic impulses in the test unit axon as judged from collision tests, and they persisted after lidocaine blockades of the nerve to the muscle. The findings are compatible with a conclusion of distal multifocal triggering of fasciculation. Fasciculating motor units had voluntary firing properties close to those of normal low-threshold motor units. Widespread fasciculations were abolished by a nonparalytic dose of a synthetic curare derivative (Pavulon) and augmented by administration of neostigmine in two cases. The fasciculations in ALS thus have the same characteristics as experimental fasciculations evoked by cholinesterase inhibitors, and there is reason to believe that the underlying pathophysiological mechanism is similar in the two cases.     

Single fibre electromyography in multifocal motor neuropathy with persistent conduction blocks

OBJECTIVE—To study theprocess of denervation-reinnervation in multifocal motor neuropathywith persistent conduction blocks in clinically affected and unaffected muscles.
METHOD—Volitionalsingle fibre electromyography (SFEMG) was performed in the extensordigitorum communis (EDC) of seven patients. The jitter, the fibredensity, and the mean interpotential interval were determined. Theresults before and after treatment with intravenous immunoglobulin(IVIg) between the unaffected EDC and affected EDC examined during thesame SFEMG session were also compared. In addition the values ofjitter, fibre density, and mean interpotential interval were analysedfor correlation with the strength score on the MRC scale, the durationof the neuropathy, the number of IVIg treatment periods, and the radialnerve conduction block values.
RESULTS—Mean jitter,percentage of jitters>60 µs, and impulse blocking percentage, werehigher than normal in both the affected EDCs and to a lesser degree inunaffected EDCs. Jitter decreased significantly after IVIg andcorrelated only with the MRC score. Fibre density and meaninterpotential interval were higher than normal equally in the affectedEDC and unaffected EDCs, but no correlation was found with strength,duration of the neuropathy, number of treatment periods, and conductionblock values.
CONCLUSION—The majorfinding is the presence of SFEMG abnormalities in clinically unaffectedEDCs. This shows a process of denervation-reinnervation even in theabsence of clinical symptoms, probably more frequent than commonlysupposed in this neuropathy. The rapid clinical improvement after IVIginfusions could be due to remyelination after demyelination and to aninterference of IVIg with the blocking effect of antibodies on theNa⁺ channels at the motor nerve endings.

     

运动神经元病的单纤维肌电图的研究

目的研究单纤维肌电图（ＳＦＥＭＧ）对运动神经元病的辅助诊断价值及探讨单纤维肌电图异常率与其病型、病情的关系。方法应用单纤维肌电图技术对４８例运动神经元病（ＭＮＤ）患者，２４例颈椎性脊髓病（ＣＳＭ）患者及４２名健康正常受试者进行研究。结果ＭＮＤ患者的ＳＦＥＭＧ阳性率为７３％，ＣＳＭ患者的ＳＦＥＭＧ阳性率为４％。结论ＳＦＥＭＧ有助于鉴别ＭＮＤ与ＣＳＭ。ＳＦＥＭＧ异常率与病型无关，与病情有关，提示ＭＮＤ存在明显的神经肌肉接头传递功能障碍。     

Activity-dependent changes in impulse conduction of single human motor axons: A stimulated single fiber electromyography study

Objective

The aim of this study is to develop a novel method to assess activity-dependent hyperpolarization in human single motor axons at a constant stimulus frequency by using intra-muscular axonal stimulating single fiber electromyography (s-SFEMG).

Methods

We performed s-SFEMG in the extensor digitorum communis (EDC) muscle of 10 normal subjects, and measured changes in latencies for single muscle fiber action potentials (MAPs) during 500 stimuli delivered at 5, 10 and 20 Hz. The data were analyzed with a repeated measurement analysis, and multiple comparisons were performed.

Results

A total of 585 MAPs were examined at 5 Hz (n = 190), 10 Hz (n = 210), and 20 Hz (n = 185) steady stimulation. There was a progressive linear prolongation of latencies, as the stimulus rate increased (F = 95.6, p < 0.001); the least square means (SEM) of latency change were 100.7 (0.28)% at 5 Hz, 102.3 (0.27)% at 10 Hz and 105.3 (0.28)% at 20 Hz. There were statistically significant differences between frequencies by Tukey–Kramer’s method. Despite the significant latency prolongation, no activity-dependent conduction block developed. A 20 Hz electric stimulation to intramuscular axons was well-tolerated in all the subjects.

Conclusions

Tetanic stimulation at a constant rate results in significant latency increase in single human motor axons, the extent of which depends on the stimulus frequency. The findings imply that physiological discharge rates will activate the Na⁺/K⁺ pump and thereby produce axonal hyperpolarization in single motor axons.

Significance

This technique may detect activity-dependent conduction block if the safety margin of impulse transmission is significantly reduced by demyelination or increased branching due to collateral sprouting in a variety of neuromuscular disorders.     

F responses studied with single fibre EMG in normal subjects and spastic patients.

Recurrent responses of single human motor neurones after antidromic activation, the so-called F response, have been studied in the abductor digiti minimi muscle in normal subjects and in spastic patients with the single fibre EMG technique. The F response occurs rarely and in groups. Half of all motor neurones did not produce any F response within an arbitrarily chosen time interval of 200 successive stimuli at 1 and 2 Hz. Spastic patients had as many silent neurones as the normal subjects but the responding neurones more frequently produced F responses (P less than 0.001). When a neurone has few responses at rest the frequency increases under activation of the contralateral or ipsilateral muscle (P less than 0.05). When there are many responses in the relaxed state there is a decrease (P less than 0.001) under activation. The behaviour of an individual neurone is consistent in different activation periods.     

Terminal intramuscular motor innervation and motor end-plates in thyrotoxic myopathy

Thyrotoxic myopathy was induced in 64 mice. Examination of their muscles revealed excessive axonal branching and degenerative changes of preterminal axons. Moreover, the mean diameter of their end-plates decreased and the levels of end-plate cholinesterase appeared to be reduced. In 43 patients with thyrotoxic myopathy, increased axonal branching and degenerative changes of preterminal axons, similar to those in the experimental mice, were also seen. The possibility that excess thyroid hormone may interfere with axonal transport or neuromuscular interactions is discussed.     

The reinnervated motor unit in man. A single fibre EMG multielectrode investigation.

Motor units in patients with motor neurone disease and polyneuropathy were studied with a new multielectrode technique allowing fibre mapping. In these disorders which are characterised by reinnervation the motor unit fibre distribution is changed from a normal scattered pattern to grouping often in clinically uninvolved muscles without definite EMG abnormalities. The changes found with this multielectrode technique in man are in accordance with those found in reinnervated motor units studied histochemically in the experimental animal.     

The normal motor unit in man. A single fibre EMG multielectrode investigation.

The motor unit in the normal EDC and biceps brachii muscle was studied with a multielectrode technique permitting recording from 44 sites 300 mum apart. It was found that the muscle fibres in man are scattered with no evidence of grouping, similar to the findings in glycogen depletion experiments in animals.     

Neuromuscular transmission in human single motor units.

A method, multiple point stimulation, has been reported to isolate 5-20 single hypothenar or thenar motor units for investigation. This method is attractive for testing neuromuscular transmission because the required stimulus intensities are much less than for supramaximal nerve stimulation, and movement artefact is less of a problem. In this investigation of controls, the changes in hypothenar and thenar motor unit surface voltage and latency of single muscle fibre action potentials belonging to the motor unit have been measured in response to trains of stimuli delivered to the motor nerve. In healthy motor units, increases in the surface peak-to-peak voltage and corresponding reductions in the peak-to-peak duration occurred, the changes being maximum at the shorter stimulus intervals and accompanied by increased synchronisation of motor unit muscle fibre action potential discharges. The investigations of the responses for healthy single motor units to repetitive stimulation provide the basis for investigations of neuromuscular transmission at the level of the motor unit in diseases of neuromuscular transmission.     

The motor unit in psychotic patients: a single fibre EMG study.

Single fibre EMG recording from extensor digitorum communis muscle is described in patients with psychotic illness. The fibre density, or average number of single muscle fibre action potentials belonging to the same motor unit within the uptake area of the electrode, was higher in the patient group than in normal controls. Increased jitter was occasionally seen. Motor and sensory nerve conduction velocity values were within the normal range. The results indicate that psychosis is associated with denervation and reinnervation by collateral sprouting.     

A comparison of the fine structure of motor end-plates in Duchenne dystrophy and in human neurogenic diseases.

With the aim of investigating the pathogenesis of Duchenne dystrophy, and in particular the role of denervation, the fine structural features of motor end-plates in the limb muscles of 13 patients with Duchenne dystrophy were compared with those in 26 controls and 50 patients suffering from known neurogenic diseases. The wide variation in control end-plates es emphasised. The sole plates in Duchenne dystrophy tended to retract from the end-plate, and shared only sprout formation, enclodure of terminals in Schwann cell cytoplasm and (in one instance) close packing of neurofilaments in the terminal with the changes in denervating end-plates. In these latter, withdrawal of terminals from the sole and various degenerative figures were the rule. It was concluded that there is no adequate morphological evidence in motor end-plates to support the concept of Duchenne dystrophy as a neurogenic disease.